3.2 Choosing a Domain Name

Choosing a domain name is more involved than it may sound because it entails both choosing a name and finding out who runs the parent zone. In other words, you need to find out where you fit in the Internet domain namespace, then find out who runs that particular corner of the namespace.

The first step in picking a domain name is finding where in the existing domain namespace you belong. It's easiest to start at the top and work your way down: decide which top-level domain you belong in, then which of that top-level domain's subdomains you fit into.

Note that in order to find out what the Internet domain namespace looks like (beyond what we've already told you), you'll need access to the Internet. You don't need access to a host that already has name service configured, but it would help a little. If you don't have access to a host with DNS configured, you'll have to "borrow" name service from other name servers (as in our previous ftp.microsoft.com example) to get you going.

3.2.1 On Registrars and Registries

Before we go any further, we need to define a few terms: registry, registrar, and registration. These terms aren't defined anywhere in the DNS specs. Instead, they apply to the way the Internet namespace is managed today.

A registry is an organization responsible for maintaining a top-level domain's (well, zone's, really) datafiles, which contain the delegation to each subdomain of that top-level domain. Under the current structure of the Internet, a given top-level domain can have no more than one registry.

A registrar acts as an interface between customers and the registry, providing registration and value-added services. It submits to the registry the zone data and other data (including contact information) for each of its customers in a single top-level domain.

Registration is the process by which a customer tells a registrar which name servers to delegate a subdomain to and provides the registrar with contact and billing information. The registrar makes these changes through the registry.

To give you some concrete examples of how this works in the real world, Public Interest Registry runs the org registry. VeriSign, Inc. currently acts as the registry for the com and net top-level domains. There are dozens of registrars for com, net, and org, including Network Solutions?a former subsidiary of VeriSign. An organization called EDUCAUSE runs the edu registry and is its only registrar. But before we get too off-track, let's get back to our story.

3.2.2 Where in the World Do I Fit?

If your organization is attached to the Internet outside of the United States, you first need to decide whether you'd rather request a subdomain of one of the generic top-level domains, such as com, net, and org, or a subdomain of your country's top-level domain. The generic top-level domains aren't exclusively for U.S. organizations. If your company is a multi- or transnational company that doesn't fit in any one country's top-level domain, or if you'd simply prefer a generic top-level to your country's top-level domain, you're welcome to register in one. If you choose this route, skip to "The generic top-level domains" later in this chapter.

If you opt for a subdomain under your country's top level, you should check whether your country's top-level domain is registered and, if it is, what kind of structure it has. Consult our list of the current top-level domains (Appendix C) if you're not sure what the name of your country's top-level domain would be.

Some countries' top-level domains, such as New Zealand's nz, Australia's au, and the United Kingdom's uk, are divided organizationally into second-level domains. The names of their second-level domains, such as co or com for commercial entities, reflect organizational affiliation. Others, like France's fr domain and Denmark's dk domain, are divided into a multitude of subdomains managed by individual universities and companies, such as the University of St. Etienne's domain, univ-st-etienne.fr, and the Danish Unix Users Group's dkuug.dk. Many top-level domains have their own web sites that describe their structure. If you're not sure of the URL for your country's top-level domain's web site, start at http://www.allwhois.com, a directory of links to such web sites.

If your country's top-level domain doesn't have a web site explaining how it's organized, but you have some idea of which subdomain you belong in, you can use a DNS query tool such as nslookup to find the email address of the technical contact for the subdomain. (If you're uncomfortable with our rushing headlong into nslookup without giving it a proper introduction, you might want to skim Chapter 12.)

To find out whom to ask about a particular subdomain, you'll have to look up the corresponding zone's start of authority (SOA) record. In each zone's SOA record, there's a field that contains the electronic mail address of the zone's technical contact.[2] (The other fields in the SOA record provide general information about the zone?we'll discuss them in more detail later.)

[2] The subdomain and the zone have the same domain name, but the SOA record really belongs to the zone, not the subdomain. The person at the zone's technical contact email address may not manage the whole subdomain (there may be additional delegated subdomains beneath), but he should certainly know the purpose of the subdomain.

For example, if you're curious about the purpose of the csiro.au subdomain, you can find out who runs it by looking up csiro.au's SOA record:

C:\> nslookup -  
Default Server:  ns1.mindspring.com

> set type=soa      Look for start of authority data
> csiro.au.         for csiro.au.
Server:  ns1.mindspring.com

        origin = zas.csiro.au
        mail addr = hostmaster.csiro.au
        serial = 2003071501
        refresh = 10800 (3H)
        retry   = 3600 (1H)
        expire  = 3600000 (5w6d16h)
        minimum ttl = 3600 (1H)

The mail addr field is the Internet address of csiro.au's contact. To convert the address into Internet email address format, you'll need to change the first "." in the address to an "@". So hostmaster.csiro.au becomes hostmaster@csiro.au.[3]

[3] This form of Internet mail address is a vestige of two former DNS records, MB and MG. MB (mailbox) and MG (mail group) were to be DNS records specifying Internet mailboxes and mail groups (mailing lists) as subdomains of the appropriate domain. MB and MG never took off, but the address format they would have dictated is used in the SOA record, maybe for sentimental reasons. whois

The whois service can also help you figure out the purpose of a given domain. Unfortunately, there are many whois servers?most good administrators of top-level domains run one?and they don't talk to each other, like name servers do. Consequently, the first step to using whois is finding the right whois server.

One of the easiest places to start your search for the right whois server is at http://www.allwhois.com (see Figure 3-1). We mentioned earlier that this site has a list of the web sites for each country code's top-level domain; it also sports a unified whois search facility.

Figure 3-1. The www.allwhois.com web site

Say you were wondering what the ad.jp domain was for. You can enter ad.jp in the text box at the top of http://www.allwhois.com/ and the web site will query the right whois server and show you the results, as in Figure 3-2.

Figure 3-2. Information about ad.jp from the jp whois server

Obviously, this is a useful web site if you're looking for information about a domain outside of the U.S.

Once you've found the right web site or the right contact, you may have found the registrar. Outside the U.S., many domains have a single registrar. A few, though, such as Denmark's dk and Great Britain's co.uk and org.uk, have multiple registrars. However, the process we've described will still lead you to them.

3.2.3 Back in the U.S.A.

In true cosmopolitan spirit, we covered international domains first. But what if you're from the good ol' U.S. of A.?

If you're in the U.S., where you belong depends mainly upon what your organization does, how you'd like your domain names to look, and how much you're willing to pay. If your organization falls into one of the following categories, you may want to consider joining us:

  • K-12 (kindergarten through twelfth grade) schools

  • Community colleges and technical vocational schools

  • State and local government agencies

That's because these organizations have historically registered under us, according to the namespace design documented in RFC 1480. In that design, a high school, for example, would register under k12.<state>.us, where <state> is the two-letter postal abbreviation for the state in which the school is located.

However, even these organizations don't need to follow this rigid structure. Many K-12 schools, community colleges, and government agencies register subdomains of org or even com. The registry that runs us has relaxed the restrictions placed on us registrants, too: now you can register in either the "locality space" (<state>.us) or the "expanded space." In the "expanded space," you could register (for example) acme.us rather than acme.co.us.

Many people, however, prefer the better-known generic top-level domains. For information on registering in one of those, read on. The generic top-level domains

As we said, there are many reasons why you might want to ask for a subdomain of one of the generic top-level domains, such as com, net, and org: you work for a multi- or transnational company, you like the fact that they're better-known, or you just prefer the sound of your domain name with "com" on the end. Let's go through a short example of choosing a domain name under a generic top-level domain.

Imagine you're the network administrator for a think tank in Hopkins, Minnesota. You've just gotten a connection to the Internet through a commercial ISP. Your company has never had so much as a dialup link, so you're not currently registered in the Internet namespace.

Since you're in the United States, you have the choice of joining either us or one of the generic top-level domains. Your think tank is world-renowned, though, so you feel us wouldn't be a good choice. A subdomain of a generic top-level domain would be best.

But which one? As of this writing, there are five open to anyone:


A new generic top-level domain


The original generic top-level domain, and the best known


A new generic top-level domain


Originally used by networking organizations, but now open to anyone


Originally used by nonprofit and other noncommercial organizations, but now open to anyone

The think tank is known as The Gizmonic Institute, so you decide gizmonics.com might be an appropriate domain name. Now you've got to check whether the name gizmonics.com has been taken by anyone, so you use an account you have at the University of Minnesota:

C:\> nslookup  
Default Server:  ns.unet.umn.edu

> set type=any           Look for any records
> gizmonics.com.         for gizmonics.com.
Server:  ns.unet.umn.edu

gizmonics.com   nameserver = ns1.11l.net
gizmonics.com   nameserver = ns2.11l.net

Whoops! Look like gizmonics.com is already taken (who would have thought?). Well, gizmonic-institute.com is a little longer, but still intuitive:[4]

[4] If you're having a hard time figuring out a good domain name, many registrars' web sites provide suggestions for free. For example, www.nameboy.com will recommend various combinations of "gizmonic" and "institute," even using rhyming words.

C:\> nslookup  
Default Server:  ns.unet.umn.edu

> set type=any                   Look for any records
> gizmonic-institute.com.         for gizmonic-institute.com.
Server:  ns.unet.umn.edu

*** ns.unet.umn.edu can't find gizmonic-institute.com.: Non-existent host/domain

gizmonic-institute.com is free, so you can go on to the next step: picking a registrar. Choosing a registrar

Choose a registrar? Welcome to the brave new world of competition! Before the spring of 1999, a single company, Network Solutions, Inc., was both the registry and sole registrar for com, net, and org, as well as edu. To register a subdomain of any of these generic top-level domains, you had to go to Network Solutions.

In June 1999, ICANN, the organization that manages the domain namespace (we mentioned them in the last chapter) introduced competition to the registrar function of com, net, and org. There are now dozens of com, net, and org registrars from which you can choose (see http://www.internic.net/regist.html).

We won't presume to tell you how to pick a registrar, but take a look at the price and any other services the registrar provides that interest you. See if you can get a nice package deal on registration and aluminum siding, for example.

3.2.4 Checking That Your Network Is Registered

Before proceeding, you should check whether or not your IP network or networks are registered. Some registrars won't delegate a subdomain to name servers on unregistered networks, and network registries (we'll talk about them shortly) won't delegate an in-addr.arpa zone that corresponds to an unregistered network.

An IP network defines a range of IP addresses. For example, the network 15/8 is made up of all IP addresses in the range to The network 199.10.25/24 starts at and ends at

A Sidebar on CIDR

Once upon a time, when we wrote the first edition of this book, the Internet's 32-bit address space was divided up into three main classes of networks: Class A, Class B, and Class C. Class A networks were networks in which the first octet (the first eight bits) of the IP address identified the network, and the remaining bits were used by the organization that was assigned the network to differentiate hosts on the network. Most organizations with Class A networks also subdivided their networks into subnetworks, or subnets, adding another level of hierarchy to the addressing scheme. Class B networks devoted two octets to the network identifier and two to the host; Class C networks gave three octets to the network identifier and one to the host.

Unfortunately, this small/medium/large system of networks didn't work well for everyone. Many organizations were large enough to require more than a Class C network, which could accommodate at most 254 hosts, but too small to warrant a full Class B network, which could serve 65,534 hosts. Many of these organizations were allocated Class B networks anyway. Consequently, Class B networks quickly became scarce.

To help solve this problem and create networks that were just the right size for all sorts of organizations, Classless Inter-Domain Routing, or CIDR (pronounced "cider"), was developed. As the name implies, CIDR does away with the old Class A, Class B, and Class C network designations. Instead of allocating either one, two, or three octets to the network identifier, the allocator could assign any number of contiguous bits of the IP address to the network identifier. So, for example, if an organization needed an address space roughly four times as large as a Class B network, the powers-that-be could assign it a network identifier of 14 bits, leaving 18 bits (four Class B's worth) of space to use.

Naturally, the advent of CIDR made the "classful" terminology outdated?although it's still used a good deal in casual conversation. Now, to designate a particular CIDR network, we specify the particular high-order bit value assigned to an organization, expressed in dotted octet notation, and how many bits identify the network. The two terms are separated by a slash. So 15/8 is the old, Class A-sized network that begins with the eight-bit pattern 00001111. The old, Class B-sized network is now 128.32/16. And the network consists of the 128 IP addresses from to

The InterNIC was once the official source of all IP networks; they assigned all IP networks to Internet-connected networks and made sure no two address ranges overlapped. Nowadays, the InterNIC's old role has been largely assumed by Internet service providers (ISPs), who allocate space from their own networks for customers to use. If you know your network came from your ISP, the larger network from which your network was carved is probably registered (to your ISP). You may still want to double-check that your ISP took care of registering their network, but you don't have to (and probably can't) do anything yourself, except nag your ISP if they didn't register their network. Once you've verified their registration, you can skip the rest of this section and move on.

It's not necessary to register RFC 1918 address space (e.g., the networks 10/8, 192.168/16). In fact, you can't since these networks are used by so many different organizations.

If your network was assigned by the InterNIC, way back when, or you are an ISP, you should check to see whether your network is registered. Where do you go to check whether your network is registered? Why, to the same organizations that register networks, of course. These organizations, called regional Internet registries, or RIRs, each handle network registration in some part of the world. In North America, ARIN, the American Registry of Internet Numbers (http://www.arin.net), hands out IP address space and registers networks. In Asia and the Pacific, APNIC, the Asia Pacific Network Information Center (http://www.apnic.net), serves the same function. In Europe, it's the RIPE Network Coordination Centre (http://www.ripe.net). And Latin America and the Caribbean are served by LACNIC, the Latin America and Caribbean Internet Addresses Registry (http://www.lacnic.net). Each RIR may also delegate registration authority for a region; for example, ARIN delegates registration authority for Mexico to a registry in that country. Be sure to check for a network registry local to your country.

If you're not sure your network is registered, the best way to find out is to use the whois services provided by the various network registries to look for your network. Here are the URLs for each registry's whois web page:









If you find out your network isn't registered, you'll need to get it registered before setting up your in-addr.arpa zones. Each registry has a different process for registering networks, but most involve money changing hands (from your hands to theirs, unfortunately).

You may find out that your network is already assigned to your ISP. If this is the case, you don't need to register independently with the RIR.

Once all your Internet-connected hosts are on registered networks, you can register your zones.

3.2.5 Registering Your Zones

Different registrars have different registration policies and procedures, but most, at this point, handle registration online, through their web sites. Since you found or chose your registrar earlier in the chapter, we'll assume you know which web site to use.

The registrar will need to know the domain names and addresses of your name servers and enough information about you to send you a bill or charge your credit card. If you're not connected to the Internet, give them the IP addresses of the Internet hosts that will act as your name servers. Some registrars also require that you already have operational name servers for your zone. (Those that don't may ask for an estimate of when the name servers will be fully operational.) If that's the case with your registrar, skip ahead to Chapter 4 and set up your name servers. Then contact your registrar with the requisite information.

Most registrars will also ask for some information about your organization, including an administrative contact and a technical contact for your zone (who can be the same person). If your contacts aren't already registered in the registrar's whois database, you'll also need to provide information to register them in whois. This includes their names, surface mail addresses, phone numbers, and electronic mail addresses. If they are already registered in whois, just specify their whois "handles" (unique alphanumeric IDs) in the registration.

There's one more aspect of registering a new zone that we should mention: cost. Most registrars are commercial enterprises and charge money for registering domain names. Network Solutions, the original registrar for com, net, and org, charges $35 per year to register subdomains under the generic top-level domains. (If you've already registered a subdomain under com, net, or org and haven't received a bill recently, it'd be a good idea to check your contact information with whois to make sure they've got a current address and phone number for you.)

If you're directly connected to the Internet, you should also have the in-addr.arpa zones corresponding to your IP networks delegated to you. (For information on IPv6 reverse-mapping, see Chapter 11.) For example, if your company was allocated the network 192.201.44/24, you should manage the 44.201.192.in-addr.arpa zone. This will let you control the IP address-to-name mappings for hosts on your network. Chapter 4 also explains how to set up your in-addr.arpa zones.

Earlier in this chapter, we asked you to find the answers to several questions: is your network a slice of an ISP's network? Is your network, or the ISP network that your network is part of, registered? If so, with which RIR? You'll need these answers to have your in-addr.arpa zones delegated to you.

If your network is part of a larger network registered to an ISP, you should contact the ISP to have the appropriate subdomains of their in-addr.arpa zone delegated to you. Each ISP uses a different process for setting up in-addr.arpa delegation. Your ISP's web page is a good place to research that process. If you can't find the information there, try looking up the SOA record for the in-addr.arpa zone that corresponds to your ISP's network. For example, if your network is part of UUNET's 153.35/16 network, you could look up the SOA record of 35.153.in-addr.arpa to find the email address of the technical contact for the zone.

If your network is registered directly with one of the regional Internet registries, contact them to get your in-addr.arpa zone registered. Each network registry makes information on its delegation process available on its web site.

Now that you've registered your zones, you'd better take some time to get your house in order. You've got some name servers to set up, and in the next chapter, we'll show you how.